This disclosure relates to the measurement of the level of a conductive liquid in a recreational vehicle wastewater holding tank.
Many recreational vehicles, such as campers, trailers, fifth wheelers, and motor homes, have one or more tanks for storing the effluent or wastewater originating in the toilet, sink, or shower. These tanks are also called black water or gray water tanks. The wastewater in these tanks is electrically conductive. Measuring the existence of a conductive path between sensor probes mounted at various levels in a recreational vehicle holding tank is a simple and cost-effective way to determine the level of fluid in the tank. The principle is that there should only be conductance between pairs of probe tips that are submerged in the wastewater.
False conductance readings caused by leakage currents from probe tips not submerged in the wastewater are a problem with systems that use conductance to measure liquid level. These leakage currents travel through the conductive residue that can build up on every surface of the tank that is exposed to the effluent, typically traveling from the non-submerged probe tip to the wall of the tank where the sensor probe is installed and then along the wall until they reach the conductive liquid. These leakage currents cause the liquid level measuring circuit to show that the tank has more wastewater in it than it actually does. Thus, the recreational vehicle owner either drains the wastewater holding tanks too frequently or ignores the readings from the level measuring circuit and runs the risk of a tank overflow. The same problem can occur in any moving wastewater tank, including but not limited to mobile environments such as boats, trains, buses, aircraft, or transportable lavatories.